Field of the Invention
Embodiments of the present application relates to the art of a control system for a hybrid vehicle in which powers of an engine and a motor are delivered to a drive shaft through a planetary gear unit.
Discussion of the Related Art
JP-A-2008-265600 describes a hybrid vehicle in which a prime mover includes a first motor, a second motor and an engine. In the hybrid vehicle taught by JP-A-2008-265600, a planetary gear unit is disposed between the prime mover and a drive shaft to distribute and synthesize torque(s). In the planetary gear unit, a sun gear is connected to the first motor, a ring gear is connected to the second motor, and a carrier is connected to the engine. Rotation of the carrier thus connected to the engine is halted by a clutch. According to the teachings of JP-A-2008-265600, a torque distribution ratio for operating the motors is determined in an energy efficient manner, and the vehicle is powered by the motors while stopping the engine and bringing the clutch into engagement.
JP-A-2012-163146 describes a vehicle drive device including oil feeding structure to a planetary gear unit. According to the teachings of JP-A-2012-163146, the oil thrown up by rotation of gears forming is collected by a catch tank, and the oil in the catch tank is caused by the gravitational force to fall down from a collected oil falling passage to be supplied into the inside housing space.
According to the teachings of JP-A-2008-265600, the hybrid vehicle can be powered by the first motor and the second motor in an energy efficient manner while halting a rotation of the carrier connected to the engine. In such dual motor mode, as indicated in the nomographic diagram shown in FIG. 9 of JP-A-2008-265600, a rotational speed of the carrier connected to the engine is fixed to 0 by bringing the brake into engagement. In this situation, output power of the motors can be increased by rotating the first motor in an opposite direction to a rotational direction of the second motor.
In the above explained dual motor mode, pinion gears of the planetary gear unit are rotated at high speed while being subjected to the output torque of the first motor. In addition, since the engine is stopped under the dual motor mode, oil supply to the pinion gears from a mechanical oil pump driven by the engine is stopped. For these reasons, temperature of the pinion gears may be raised excessively to cause seizure and wear. However, in the hybrid vehicle taught by JP-A-2012-163146, the pinion gears thus rotated at high speed in the dual motor mode cannot be cooled and lubricated. Even if the lubrication system taught by JP-A-2008-265600 is employed in the hybrid vehicle taught by JP-A-2012-163146, the pinion gears may not be lubricated sufficiently when rotated at high speed and consequently the planetary gear unit may be damaged.
Such seizure and wear of the pinion gears may be prevented by propelling the vehicle only by the second motor instead of propelling the vehicle by both motors while halting the carrier. However, an output range of the motors has to be restricted and hence driving performance of the hybrid vehicle may be limited.